The present invention relates to a high speed coagulation-flocculation and sedimentation method for treating waste water and particularly to a novel high speed coagulation-flocculation and sedimentation method for treating waste water, which permits a speedy treatment of waste water including stormwater runoff and also permits a valuable reuse of the sludge produced in the course of treatment.
Generally, the waste water is discharged after it was purified through a series of treatment steps in a waste water treatment station including a sewage treatment station, nightsoil treatment station and the like, wherein the waste water is first freed of the solid matter, floating matter, fatty matter and the like and then is subjected to a secondary or tertiary treatment as required by a desired water quality standard.
The water purified through such treatments should meet the required quality criteria, wherein the quantity of nitrogen and phosphorus which act as important factors for the eutrophication of the water is no less important than BOD, COD or the like. Because particularly the phosphorus of them is contained much higher in quantity in the influent water along with stormwater runoff from the ground surface than in the waste water itself, its effective removal calls for not only the treatment of the waste water resulting from point sources of contamination but also the treatment of stormwater runoff streams. However, the conventional waste water treatment processes mostly depended on a normal activated sludge process or extended aeration process, wherein the removal efficiency in term of total phosphorus amounted to so low as 10-30%. In addition, there was caused a problem, specially because the stormwater runoff streams at the time of rainfall were left to discharge without treatment.
On the other hand, as a most effective method of removing the phosphorus in the waste water, there is widely used the coagulation-flocculation and sedimentation method based on the use of coagulant. However, this method is associated with a problem in that an additional cost is required to treat the sludge which is inevitably produced as the result of the process and furthermore a secondary environmental pollution due to the sludge is caused.
The object of the present invention, which invention was created to resolve the above-described problems of the conventional art, is to provide a method for treating waste water based on a high speed coagulation-flocculation and sedimentation which permits a high speed treatment of waste water including stormwater runoff and an effective removal of phosphorus and also permits a valuable reuse of the sludge produced in the course of waste water treatment.